into it, and in two and one-half hours reached more than half way to the opening (Fig. 7, Pl. IV). A new sporangium may be formed when, or soon before the filament has grown through the old sac, or, as in some Saprolegnia since studied, the filament may produce even a greater growth after than it had made before the formation of the first sporangium. I found a form growing on some very small bull-heads, which after the first sporangium had developed, sent out, in many cases noticed, a very extended and branching growth. They were specimens preserved for study by being placed in a cell and kept irrigated.'

The form just referred to as growing upon small specimens of fish, and of which I was enabled to study out the parthenogenetic forms, was peculiar in having the zoospores differing greatly in size, for, in the same sporangium, it varied from .or mm. to .021 mm. in diameter, the sporangia averaging about .04 mm., and the filament .025 mm. in size. There were also invariably a few zoospores remaining in the old sac after it had opened, the cause of which was that a large zoospore was unable to pass through the opening, thus keeping back all the remaining zoospores until they had settled down to the spherical form. The new filament is always constricted where it passes the opening of the sac, showing that it thus entirely closed it, holding the zoospores in a pouch. on the side of the filament. The zoospores developed in each case were much less numerous than I have seen in any other specimens, there being from ten to eighteen in each sporangium. In some of the sacs which had been opened but a short time, there was an infusorian nearly twice the size of the largest zoospore. They must have passed in through the openings of the sporangia, and were unable to make their exit.

In studying, and especially in growing these forms, one can but notice the rapidity with which they develop, especially under favorable conditions. Illustrating this point I introduce the following table which embraces the results of timing the

"I find that a very satisfactory way to keep growing specimens in a fresh condition under a cover glass, is to place the slide by the side of a watch-glass of water, and, taking a short thread thoroughly moistened, place one end in the watch-glass, and apply the other closely to the edge of the cover-glass. If not placed under a bell jar evaporation will be sufficient to allow a supply of fresh

water.

growth of a young and thrifty filament under a magnifying power of 200 diameters. For the first hour observations were taken every five minutes; during the second, every ten minutes, after which the time varied. The first column represents the time of measurement, and the second the length of fila

From these data it will be seen that growth for the first hour averaged 6.5 mm.; for the second, 7.64 mm., and for the third about 6 mm.; this, it will be remembered, under a magnifying power of 200 diameters. Growth during the remainder of the day averages a considerable less, but judging from the appearance of the plant at 8 o'clock the next morning, I think that growth had taken place as rapidly as when the first measurements were taken. The branches shown were given off at 10.07 and 10.42 o'clock, and averaged 7.8 mm. per five minutes. The time required for a plant to develop fruit from the zoospore varies greatly with varying conditions. A mat of mycelium, from which the specimen was taken, developed fruit in four days, but this time was rather long when compared with other observations made on the same germs, considering that the mycelium was already well developed. In one case zoospores were placed upon a slide with a small fragment of a fly, the first sporangium opened in about thirty hours, and the second one on the same filament eight hours later. I have not yet made any satisfactory observations on the second mode of reproduction in this genus, but according to the best authorities on this group, it is in principle very similar to that described further on, under the genus Achlya. The number of times that this unsexual form may be produced without the intervention of sexual reproduction, or in a single vegetation period, I have not been able to ascertain. A series of experiments bearing partially upon this point, and showing a

great variation in the form of the sporangia have just been made. In August, 1878, a triton was so injured in being caught that a portion of the liver passed out from the body cavity and hung from the side of the abdomen. In this condition it was placed in jar with some small fishes and allowed to remain. Observations made a few days later showed the appearance of filaments from the injured portion, and in two days later fruit was produced.

The sporangia and zoospores had the characters of the genus Saprolegnia; but differed from those already described, in forming the new sporangium to one side of the old-the filament elongating only sufficiently for the formation of the sporangium; about thirty hours later, other specimens were carefully removed and examined. The filaments had elongated to varying lengths beyond the old sacs and formed sporangia (Pl. v., Fig. 2), very similar to those which characterize the germs Dictynchus, Leitgeb. The zoospores, instead of raising out through an opening in the apex of the sporangium, burst through the side, leaving behind a clear membrane of its former size and shape. In the genus Dictynchus, the sporangium emptied of zoospores appears as if divided into many angular transparent cells, while in the form noted the old spore case remained rounded. Fig. 2, Pl. v., represents a filament bearing three of these sporangia, the lower one yet containing the zoospores. The sporangia varied from .04 mm. to .41 mm. in length, and in some cases the branches contained but a single row of zoospores.

August 30th, four days after the first triton was caught, another was taken and an incision carefully made in the side of the abdomen, allowing a portion of the intestines and liver to pass out uninjured. It was placed in a jar of water, which was kept changed by means of a siphon, and sown with spores from the first specimen. At 10 o'clock, Aug. 31st, the intestine had a delicate velvety appearance, caused by a very dense growth of filaments about .5 m m. long; at 4 o'clock P. M., the filaments were 2 mm. long, unbranched and bore no traces of sporangia. Sep. 1st, 10 o'clock, an occasional ripe sporangia was found, and Sep, 2d, 10 A. M., many; here also the new sporangium was formed on the filament to one side of the old; later observations showed that none of the Dictyo-sporangia were produced; the late sporangia, one or more formed on the same

filament, were ovate .064 mm. long by .041 mm. broad, and opened at one side near the top by a short, or, frequently, quite long tube. (Figs. 6 and 7. Pl. v).

They required a much longer time to develop fruit than in the first case. The zoospores were all distinct from each other .009 mm. in diameter, and generally underwent a rejuvenescence. The triton died in four days, but observations were made until the plant ceased to grow, and no sexual fruit was produced. Sep. 5th, a third triton was placed under the same conditions as the second, and sown with fruit grown on the second, the time of the appearance of the plant and its development was nearly the same as in the former instance; the new sporangia however were produced as in the first forms described . (Pl. v. Fig. 1), and the late forms were the same as in the former experiment, and in both cases the intestine had decayed and broken away. The triton died in three days. Sep. 10th, the egg sac of a fourth triton was exposed and sown with zoospores from the third experiment. The Saprolegnia dedeveloped were the same as in the last case. In six days the portion bearing the fungus was separated from the main part of the ovary by the growth of a transparent membrane closing the body cavity. Since then no filaments have appeared, and now the triton seems to be in good condition for another operation.

Although these experiments were not successful as far as the production of oogonia is concerned, they are of considerable importance as showing the great variability of the parthenogenetic forms in different generations and different stages of growth; also the fact of their attacking healthy parts, although in an unnatural condition, and causing their decay.

Concluded in our next issue.

THE "OIL

IMMERSION" OF CARL ZEISS COMPARED WITH THE OBJECTIVES OF

C. A. SPENCER & SONS.

BY PROF. H. L. SMITH, lld.

Some four months ago I sent two objectives, by special request, one to Belgium, the other to Germany. They were. made by C. A. Spencer & Sons, and were their then highest

grade, having a balsam angle of about 102°. I say their then highest grade, as they have since brought out a fth, and also ath, on a new formula having a balsam angle of near 110°. One of the objectives sent to Germany was compared with the new "Zeiss Oil Immersion" by a personal friend of mine, not the owner of this objective; he pronounced it an excellent glass, but, to use his own words, "a long way behind his Zeiss Oil Immersion." I felt inclined to accept this decision, though the Messrs Spencer assured me, that there must be some mistake; yet, from the very high reputation of M. Zeiss, and especially from his connection with Professor Abbe, in the production of the new objective, I was prepared to admit that he had, really, made something of surpassing excellence, which would easily beat any competitor. True, Mr. Dallinger's report upon this objective showed that, upon the whole, the new optical wonder of Jena did not quite equal the Powell and Leland" 8th new formula," but then I had not seen any of these new formula objectives of the world-renowned English opticians, and as the same able and wholly competent judge had decided that Mr. Tolles' %th was not quite up to this "new 8th " though pressing it very closely, I felt inclined to believe that, really, M. Zeiss had stolen a march on the Americans. For the purpose then of satisfying myself, and for the grim satisfaction of convincing the Messrs. Spencer, I purchased in London a "th" immersion by Zeiss, with the express notice that it was to be tested against the best American objectives, and more recently induced a friend, who had just received the "new oil immersion 8th" to send me that for examination. The th proved to be a good objective. I did not feel like complaining that I had not the worth of my money, but it was not so good an objective as I could have procured from either Tolles, or Spencer, though of higher numerical grade than they would have furnished for the same money. It proved certainly, that M. Zeiss was an excellent workman, and as I have said I did not feel disposed to think I had paid too high a price, as Franklin has it, " for the whistle;" but I did expect to see something far superior to the th when the "oil" should arrive. This indeed proved to be the case, and I have no hesitation in saying, and all who have looked through it here agree with me, that up to this time, the new Zeiss "%th Oil Immersion " is the best foreign made objec